Ephialtes of Trachis

Ephialtes of Trachis (died 470 BC) was a Malian Greek warrior whose betrayal of King Leonidas I at the Battle of Thermopylae led to the defeat of the Greek army.

Biography
Ephialtes of Trachis was born in Trachis, Malis, the son of Eurydemus. During the Battle of Thermopylae in 480 BC, Ephialtes, who knew the land around Thermopylae well, decided to sell out his fellow Greeks to the Persians in exchange for a reward from King Xerxes I. He showed them a mountain pass around the Spartan army which allowed for them to flank and massacre the Spartans and their king, Leonidas I, who stabbed him with the tip of his spear as Ephialtes ran Leonidas through with his sword. Ephialtes survived, and Xerxes I rewarded him well, but the Persian defeat at the Battle of Salamis led to Ephialtes fleeing to Thessaly. There, the Amphictyons of Pylae hired an assassin to murder Ephialtes in revenge for his betrayal of Greece.